Electromagnetic induction apparatus



y 7, 1966 A. v. HUGHES 3,252,118

ELECTROMAGNETIC INDUCTION APPARATUS Filed June 2, 1958 2 Sheets-Sheet 1INVENTOR.

May 17, 1966 A. v. HUGHES 3,252,118

ELECTROMAGNETIC INDUCTION APPARATUS Filed June 2, 1958 2 Sheets-Sheet zINVENTOR.

) FrfZz/r United States Patent 3,252,118 ELECTROMAGNETIC INDUCTIONAPPARATUS Arthur V. Hughes, Bloomfield Township, Oakland County, Mich.,assignor to Kuhlman Electric Company,

Troy, Mich, a corporation of Michigan Filed June 2, 1958, Ser. No.739,232 16 Claims- (Cl. 336-213) This invention relates toelectromagnetic induction ap paratus and more particularly to animproved wound electromagnetic core for such apparatus.

In the manufacture of certain types of electromagnetic inductionapparatus, it has proved to be advantageous to utilize preformedelectrical conductive windings and to assemble the core to and uponthose windings. It has further proved to be advantageous, particularlyin conjunction with preformed windings, to form the core of wound, coldrolled steel strip.

In the general prior practice, a strip of cold rolled steel having apreferred direction of magnetization is wound upon a mandrel to form aspiral, and the wound core is then heat-treated to establish thepermanent set of the metal, to relieve the internal'strains and toimprove the magnetic properties.

In one prior method of assembling the core to the electrical windings,the spiraled strip is rewound, in its entirety, into and on thepreformed electrical winding.

To facilitate the assembly operation and to reduce the likelihood thatthe magnetic properties of the steel will be impaired due to working ofthe metal during assembly of the core to the conductive winding, it hasfurther been suggested that the core strip be severed, during unwinding,into a plurality of sections, and thereafter assembledsection-by-section upon the core, each section being placed inend-abuttingrelation with the preceding section.

It has been recognized, however, that such s'ectionalizing of the coretends to impair the magnetic qualities unless pains are taken to insurethat the air gaps at the end abutments are adequately bridged bylow-reluctance magnetic paths. Accordingly, it has further beensuggested that the wound core be formed into sections which are pluralturns in length, or that the sections be one or less turns in length,with the joints being staggered. The

former method permits all of the sections to be formed into equal (e.g.,2, 2%, 3) turn-lengths and allows appreciable bridging of the buttjoints, but requires the manipulation of plural turn-lengths of stock,retarding the speed of assembly and, again, leading to a danger ofimproper working of the stock subsequent to annealing. The latter methodfacilitates assembly, but requires that the core sections havesubstantiallydiffering turn-lengths if'the joints are to be staggered toan adequate degree to provide proper bridging or shunting of the airgaps.

The present invention relates to an improved core of the wound type andto an improved method for constructing such cores. By virtue of theimproved construction, the core can be. formed of relatively short andeasily handled sections, most of the sections can be of equalturn-lengths, and adequate bridging can be obtained at each of the endabutments. Further, the cross section' of the core legs can besubstantially constant.

In accordance with certain of the principles of the present invention,an electromagnetic induction apparatus is provided with an electricalwinding structure and a magnetic core structure in linkinginterrelationship, with the core structure comprising a plurality ofwound, pieced, interleaved-spiral magnetic strips. Each turn of each ofthe plural strips is separated from any other turn of that strip by aturn of at least one other strip, and each strip is formed of aplurality of discrete individual portions, each of those portions beingin end-abutting relation with 3,252,118 Patented May 17, 1966 Ice-abutment of one of the spiral strips and the end abutment of theadjacent turn preferably being at least onequarter of a turn-length soas to insure proper shunting of the high-reluctance air gap with alow-reluctance path. In one embodiment of the invention, most of theendabutment air gaps are shunted on both sides by portions of anotherspiraled strip or of other spiraled strips, while in one of theembodiments of the invention, bilateral multilayer bridging is provided,that is, each such end abutment is magnetically bridged by a pluralityof portions of other strips on each side.

In the preferred practice, the end abutments of any one of the stripsare substantially aligned radially of the core while the end abutmentsof a second spiraled strip are aligned along another and remotely spacedradius of the core structure. The radial alignment of the end abutmentsof each strip in this fashion permits the turnlength of the individualcore sections to be constant, facilitating both manufacture andassembly.

In order to construct a core embodying theprinciples of the presentinvention, a plurality of face-abutting strips of magnetic material areconcurrently wound upon an arbor so as to form interleaved spirals inthe nature of a bifilar winding. In the preferred procedure, the woundcore is then heat-treated. Thereafter the intercoiled strips areunwound, Without disturbing the permanent set and the plural strips aresevered, as by shearing, at dilierent spaced-apart locations during theunwinding so as to divide each of the strips into a plurality of stripportions. Desirably, but not imperatively, each of substantially all ofthe sections of each of the spirals is equal in turn-length to theothers, so as to facilitate the shearing operation and the subsequentassembly operation.-

Subsequent to the shearing operation, the strips are appropriatelystacked and arethen assembled upon the electrical winding structure intheir original, wound, interleaved spiral relationships. Since butrelativelyshort lengths of stock are assembled to the winding structure,it is simpler to avoid excessive distortion of the strip during itsinsertion through the electrical winding struc ture.

A'more complete understanding of the core structure, of the method ofmanufacturing of'the .core, and of the other principles of the presentinvention may be obtained from a consideration of the following detaileddescription of embodiments of the invention when read with reference tothe accompanying drawings in which:

FIGURE 1 illustrates a partially completed electromagnetic inductionapparatus embodying certain of the principles of the present invention;

FIG. 2 shows the core of the apparatus of FIG. 1 at one stage in itsconstruction;

FIG. 3 illustrates the core of FIG. 2 at a later stage in itsconstruction as Well as shearing equipment for severing the core stripsinto sections; 7

FIG. 4 is an enlarged view of the assembled core of FIG. 1;

FIG. 5 is a view of a modified form of assemble-d core; and

FIG. 6 is a view of the core of FIG. 5 at one stage in its constructionalong with a showing of shearing means for severing each of the pluralstrips of core material into sections. I

In the electromagnetic induction apparatus represented in FIG. 1, a corestructure 10 is electromagnetically and mechanically linked with a pairof electrically conductive winding structures 12 and 14 each of which ispreformed preformed winding structure is common to two cores 10.

In the arrangement of FIG. 1, the core is formed with a generallyrectangular window so as to establish the maximum space factor inrelation to the cylindrical (here of generally rectangularcross-section) preformed winding structures.

The core 10 of FIG. 1 comprises a plurality of pieced,interleaved-spiral magnetic strips, two such strips being employed inthe embodiment of FIGS. 1 through 4 of the drawings. To construct such acore, two lengths of cold rolled strip steel of appropriate magneticcharacteristics, width and thickness (normally about twelve thousandthsof an inch) are brought into face-abutting relationship and wound upon amandrel 16 (FIG. 2). While the mandrel 16 may be stationary and the twoface-abutting strips wrapped around the mandrel, the more advantageousprocedure is to align and face-abut the two strips 18 and 20, to secure,in any appropriate fashion, their respective ends 22 and 24 together andto one point upon the surface of the mandrel 16, and then to rotate themandrel about the axis of the mandrel shaft 26, delivering the twostrips approximately tangentially to the point of engagement with themandrel. The incoming strips are or may be normally tensioned to aselected degree (with or without the application of radial pressure atthe point of tangency) to provide the requisite tightness and/or shapeof core.

It has previously been recognized that in cores which are wound, unwoundand assembled to the conductive winding structure, the creepage of theturns of the core from their initial, Wound positions during assembly ofthe core to the conductive winding structure produces misalignment whichrenders the assemblyof the core to its original form very difiicult. Toprovide space to accommodate this creepage, spacers may be disposedbetween the turns during the winding operation. These spacers can beelements extending but a small portion of the turnlengths, but it hasbeen found to be preferable to utilize string, fabric or othercombustible materials which are coextensive with and lie parallel withthe turns. Thus, one or more pieces of string or strips of combustiblematerial can be placed on top of, between, or beneath (or anycombination thereof) the two incoming aligned strips of material so thatthe combustible material is wound concurrently with the steel stripsupon the mandrel 16.

As illustrated, a rectangular mandrel is employed in view of the assumedconfiguration of the preformed conductive winding means 12 and 14 (FIG.1). Consequently, each turn is generally rectangular, having fourstraight leg portions and four right-angle turns, with each such turnbeing upon a radius.

Subsequent to the winding operation as illustrated in FIG. 2, the coreis heat-treated to anneal it and to destroy the combustible spacingmaterial, if such was employed. Thereafter, the woundcore is carefullyunwound and the component spiraled strips are each severed into aplurality of sections, care being taken-during this operation to avoidoverstressing the annealed turns of the core. To perform this operation,the shaft 26' (FIG. 3) of the mandrel 16' (which may as a matter ofmanufacturing convenience but need not be the same elements as shaft 26and mandrel 16 of FIG. 2) is rotatably supported so that the core 10 maybe rotated about the axis of that shaft with the two strips of magneticmaterial 18 and 20 being drawn therefrom. The inner strip 18 is trainedthrough a severing means 28 while the strip 20 constituting the outerspiral is trained through a severing means 30. Severing means 28 and 30may be of any suitable well known type and it has been found to besatisfactory, with the subject construction, to employ shearingequipment, obviating the requirement of certain of the prior-artconstructions for a sawing operation.

In this connection, it is to be understood that the term turn-length isintended to connote the length of any turn of the strip stock of thecore, that is, one full turn of the strip even though the actual lengthof the strip required to complete one full turn will vary between theinner and the outer turn of the core due to the buildup.

Similarly, a half turn-length is the length of strip stock required atany point in the build-up to complete 180 of winding of the core and twocore lengths is the amount of strip stock, at any point in the build-up,required to complete 720 or two full turns of the core.

In the arrangement illustrated in FIG. 3, strip 18 is first severed atpoint 36 to form a portion or section 38 one-half turn-length long.Strip'18 is next severed at point 40 so as to produce a portion 42 oneturn-length long. Strip 18 is thereafter sheared or otherwise severedeach one turn-length. Strip 20 is first sheared at point 44 to form aportion 46 which is one turn-length long and is next sheared at point 48to form to a portion 50 which is also one turn-length long. Thereafter,strip 20 is cut into one turn-length sections. In the particularstructure which is illustrated, the final cut of strip 18 will produce aone-half turn-length innermost section, while the final cut of strip 20will produce a one turn-length final section Following the severingoperation, the portions are stacked in succession for convenience instorage and re assembly. Thereafter, the core portions are reassembledin their wound, interleaved spiral relationship about the conductivecoil structure. The'reassembled core is illustrated (with the conductivewinding structure omitted for clarity) in the enlarged view of FIG. 4.

In the assembly of the core 10 to the conductive winding structure, theinnermost portion 52 of strip 18 is first placed inside the winding coilstructure. innermost section 54 of strip 18 is then placed inendabutting relationship with portion 52, the end abutment 55 occurringat the top of the core structure in the illustration of FIG. 4. Theinnermost section 56 of strip 20 is then slipped between core portions52 and 54, its innermost end 24 aligning with the'innermost end 22 ofthe strip portion 52. Portion 56 extends to point 58, at the bottom legof the core in the showing of FIG. 4, and the next step in the preferredassembly sequence is to bring section or portion 60 of the strip 20 intoabutment with the portion 56 at junction 58. Thereafter, the nextportion 62 of strip 18 is slipped between portions 56 and 60 of strip 20with the inner end of strip 62 being brought into abutment with theouter end of strip 54 at point 64.

The building up of the core into its reassembled relationship proceedsin this fashion, terminating with the placing of the outer portion 46 ofstrip 20 over the outer portion 38 of the strip 18. The completelyassembled core is then secured in position in any suitable, well knownfashion.

While the end abutments of the strip 20 including abutments 44, 48 and58 are shown to be radially aligned, and while the end abutments of theinner spiraled core strip 18, including abutments 55, 64, 40 and 36 areshown to be aligned along a radius spaced from the line of the abutmentsof strip 20, it will be recognized that it is not imperative to thepractice of all of the principles of the invention that the abutments ofeither strip be in alignment or that the 180 spacing be employed.However, as noted hereinbefore, it has been found to be advantageousfrom a number of standpoints to construct the core in this fashion.

It will be observed in the enlarged showing of FIG. 4 that except forthe innermost abutment 55 and the outermost abutment 44, each endabutment or joint in the structure is bridged on both sides by a stripof magnetic material which extends a very substantial distance in bothThe second directions from the gap so as to insure that a W- reluctancebridge is established. Thus, in the illustrated arrangement, thebridging strips, in each case, are continuous for 180 in both lengthwisedirections from the P- FIG. 5 of the drawings illustrates a reassembledcore structure (with the conductive winding now shown) in which threestrips of magnetic steel are utilized to form three interleaved spiralsand FIG. 6 shows a step in the construction of the core of FIG. 5. Inthis modification, three strips of steel are brought into face-abuttingrelationship and wound upon a mandrel in the manner above discussed inconnection with FIG. 2. After annealing, the three interleaved spiralwindings are unwound and each strip is severed into a plurality ofportions or sections during the unwinding operation, as-illustrated inFIG. 6.

In the illustrated arrangement, the outer strip 70 is first severed atthe one turn-length point 72 to form the portion 74 and is thereaftersheared each one turn-length. The intermediate strip 76 .is firstsheared at point 78 to define a one-quarter turn-length portion 80 andis thereafter cut into one turn lengths. The innermost strip 82 is firstsevered at point 84 to define a one-half turn-length portion 86 and isthereafter severed into one turn-length portions.

In reassembling the strip portions about the conductive windingstructure, the innermost portion 94 is first placed within theconductive winding structure, this portion being one-half turn in lengthand terminating at abutment 96. Next, portion 98 of strip 82 is placedin end-abutting engagement with portion 94 at abutment 96. Core elementsor portions 100 and 102, the innermost portions of strips 76 and 70,respectively, are then slipped between portions 94 and 98, theirinnermost ends being aligned with the innermost end of section 94. Itwill be observed that core portion 100 is three-quarters of aturn-length long (270) and hence terminates along the left-hand verticalleg of the core at junction 106 and that portion 102 is one turn-lengthlong (360) and hence terminates vat junction 108 along the bottom leg ofthe core.

Portion 110 of strip 82 is then placed in end-abutting relationship, at106, with portion 100, and portion 112 of strip 76 is placed inend-abutting relationship, at 108, with portion 102. Succeeding stripportions are assembled in this fashion to complete the core.

In the core of FIG. 5, it will be observed that except for the innermostand outermost end abutments, each of the end abutments is bridged onboth sides by a multiple layer of metal strip, each of the end junctionsbeing representatively bridged by two layers of the strip steel at eachside. Further, the bridging steel does not, in the disclosedarrangement, itself have a junction for at least 90 so that an excellentlow-reluctance bridging or shunting path is provided for each of the airgaps which tend to exist at the end abutments, still further improvingthe magnetizing current characteristics in the vicinity of the joints.

The principles of the construction can be extended to four, five or ninterleaved spiral strips. If the preferred practice above described isfollowed, the gaps in the four, five or n spiral paths will appear atfour, five or n points along the magnetic path.

It is reiterated that it is not imperative to the practice of theprinciples of the invention that the end abutments in any one of thestrips be aligned but that they'may be staggered if desired, and itshould further be noted that each of the strips illustrated in FIGS. 4and 5 of the drawings may, if desired, actually be made up of pluralcomponent strip thicknesses. In that event, it is also not imperativethat an equal number of metal thicknesses be employed to form each ofthe strips, that is, the number of constituent elements forming one ofthe spirals may be different than the number of metal thicknessesconstituting another one of the spirals.

It will also be observed that the principle of concurrently winding aplurality of strips in interleaved spirals can also be applied to themanufacture of cores in which the strips are not pieced, possessing theadvantage that the length of the material, with n interleaved spiralstrips of a given thickness, which would have to be threaded through thewinding structure to obtain a desired core thickness would be l/n of thetotal length which would be requiredif the entire core were formed of asingle strip of the same thickness, as in the prior practice.

' While it will be apparent that the embodiments of the invention hereindisclosed .are well calculated to fulfill the objects of the invention,it will be appreciated that the invention is susceptible tomodification, variation and change without departing from the properscope or fair meaning of the subjoined claims.

What is-claimed is:

1. Electromagnetic induction apparatus comprising an electrical windingstructure and a magnetic core structure in linking interrelationship,said core structure comprising a plurality of wound, pieced,interleaved-spiral magnetic strips.

2. Electromagnetic induction apparatus comprising an electrical windingstructure and a magnetic core structure in linking interrelationship,said core structure compris-.

ing a plurality of pieced, interleaved-spiral magnetic strips, each turnof each of said strips being separated from any other turn of said stripby a turn of at least one other strip.

3. Electromagnetic induction apparatus comprising an electrical windingstructure and a magnetic core structure in linking interrelationship,said core structure comprising a plurality of wound, pieced,interleaved-spiral magnetic strips, each of said strips being formed ofa plurality of discrete individual portions, each of said portions ofany one strip end-abutting another one of said portions of said any onestrip.

4. The combination of claim 3 in which most of said portions are oneturn in length.

5. Electromagneticinduction apparatus comprising an electrical windingstructure and a magnetic core structure in linking interrelationship,said core structure comprising a plurality of wound, pieced,interleaved-spiral magnetic strips, each of said strips being formed ofa plurality of discrete individual portions in successive end-abuttingrelationship, most of said end abutments being bridged by portions ofanother one of said strips.

6. Electromagnetic induction apparatus comprising an electrical windingstructure and a magnetic core structure in linking interrelationship,said core structure comprising a plurality of wound, pieced,interleaved-spiral magnetic strips, each of said strips being formed ofa plurality of discrete individual portions in successive endabuttingrelationship, each of said end abutments being bridged by a portion ofanother one of said strips.

7. Electromagnetic induction apparatus comprising an electrical windingstructure and a magnetic core structure in linking interrelationship,said core structure comprising a plurality of wound, pieced,interleaved-spiral magnetic strips, each of said strips being formed ofa plurality of discrete individual portions in successive endabuttingrelationship, each of said end abutments being bridged on both'sides byportions of another one of said strips.

8. Electromagnetic induction apparatus comprising an electrical win-dingstructure and a magnetic core structure in linking interrelationship,said core structure comprising a plurality of wound, pieced,interleaved-spiral magnetic strips, each of said strips being formed ofa plurality of discrete individual portions in successive endabuttingrelationship, each of said end abutments being bridged by multiplelayers of magnetic strip.

9. Electromagnetic induction apparatus comprising an electrical windingstructure and a magnetic core structure in linking interrelationship,said core structure comprising a plurality of wound, pieced,interleaved-spiral magnetic strips, each of said strips being formed ofa plurality of discrete individual portions in successive endabuttingrelationship, each of said end abutments being bridged on both sides bymultiple layers of magnetic strip. 10. Electromagnetic inductionappartus comprising an electrical winding structure and a magnetic corestructure in linking interrelationship, said core structure comprising aplurality of wound, pieced, interleaved-spiral magnetic'strips, each ofsaid strips being formed of a plurality of discrete individual portionsin successive endabutting relationship, each of said end abutments beingbridged on each side by portions of two other ones of said strips.

11. The combination of claim 10 in which most of said portions are oneturn in length and in which the end abutments of any one of said stripsare substantially aligned radially of the core.

12. The combination of claim 10 in which the end abutments of one ofsaid strips are circumferentially spaced about said core structure fromthe end abutments of another one of said strips.

13. The combination of claim 12 further characterized in that the endabutments of said one strip are aligned radially of said corestructure'and in that the end abutments of said other strip are alignedalong another radius of said core structure.

14. Electromagnetic induction. apparatus comprising an electricalWinding structure and a magnetic cores-tructure in linkinginterrelationship, said core structure comprising a plurality of wound,pieced, interleaved-spiral magnetic strips, each of said strips beingformed of a plurality of discrete individual portions in successiveendabutting relationship, each of said end abutments being bridged onboth sides by portions of another one of said strips, most of saidportions being one turn in length.

15. Electromagnetic induction apparatus comprising an electrical windingstructure and a magnetic core structure in linking interrelationship,said core structure comprising a plurality of wound, pieced,interleaved-spiral magnetic strips, each of said strips being formed ofa plurality of discrete individual portions in successive enabuttingrelationship, each of said one abutments being bridged by multiplelayers of magnetic strip, most of said portions being one turn inlength.

16. The combination of claim 12 further characterized in that the endabutments of said one strip are aligned radially of said core structureand in that the end abutments of said other strip are aligned alonganother radius of said core structure, most of said portions being oneturn in length.

References Cited by the Examiner UNITED STATES PATENTS 2,305,649 12/1942Vienneau 336213 2,305,650 12/ 1942 Vienneau 29155.5 2,380,300 7/1945Gaston 29-1555 2,927,366 3/1960 Link 336----213 X JOHN F. BURNS, PrimaryExaminer.

MILTON O. HIRSHFIELD, ORIS L, RADER,

Examiners.

1. ELECTROMAGNETIC INDUCTION APPARATUS COMPRISING AN ELECTRICAL WINDINGSTRUCTURE AND A MAGNETIC CORE STRUCTURE IN LINKING INTERRELATIONSHIP,SAID CORE STRUCTURE COMPRISING A PLURALITY OF WOUND, PIECED,INTERLEAVED-SPIRAL MAGNETIC STRIPS.